At present, highly activation of olefin polymerization catalysts is the most important problem. Since copolymerization with polar monomers and aqueous-system polymerization have recently been made possible, olefin polymerization catalysts composed of late transition metal complexes have attracted attention.
In particular, it has been reported that nickel catalysts (Shell Higher Olefin Process catalyst: SHOP catalyst) having a fluorohydrocarbon group near an oxygen atom and an ester group near a phosphorus atom exhibit high ethylene polymerization activity even in an aqueous system (Patent Document 1 and Non-patent Documents 1 and 2).
It has also been reported that chlorine-containing nickel catalysts (Shell Higher Olefin Process catalyst: SHOP catalyst) represented by general formula (5) or (6) exhibit high ethylene polymerization activity even in an aqueous system (Patent Document 2 and Non-patent Document 3).
(wherein Ph represents a phenyl group).
However, the activity and molecular weights of the resulting polymers are unsatisfactory for practical use, and development of new catalysts has been demanded.
[Patent Document 1] WO02/24763
[Patent Document 2] DE2923206A1
[Non-patent Document 1] Macromolecules, 2001, vol. 34, p. 2438
[Non-patent Document 2] Macromolecules, 2001, vol. 34, p. 2022
[Non-patent Document 3] Macromolecules, 2003, vol. 36, p. 6711